This application pertains to the art of controlling the introduction of medications to patients in response to the patient's physiological conditions or responses. The invention is particularly applicable to apparatus for automatically controlling a patient's blood pressure through automatic adjustments in the infusion rate of a blood pressure controlling medication in response to samplings of the patient's blood pressure and will be described with particular reference thereto. However, it will be appreciated that the invention has other applications such as infusing medications to control other physiological conditions including pulse rate, pulmonary rate, levels of body secreted substances in the blood, and the like.
Commonly, the postoperative care of cardiac surgery patients includes the administration of medications to maintain a consistent and non-hypertensive blood pressure level. This is commonly accomplished by the titration of a vasodilating medication such as Nipride. By controlling the infusion rate of Nipride, the patient's peripheral resistance can be regulated which permits control of the patient's blood pressure levels.
The infusion of Nipride is accomplished with an adjustable infusion pump. The adjustment of the medication infusion rate of the infusing pump is a complicated procedure carried out by the attending nurse. The attending nurse selects an approximate infusion rate and observes the effect on the patient's blood pressure. From the change in the patient's blood pressure level, the nurse determines a change or correction to the infusion rate. This process continues in an attempt to reach a blood pressure level which is close to a preselected, desired blood pressure level.
Many variables make this procedure both difficult and inefficient. Physiological factors influence the blood pressure levels of the patient, in some instances causing the pressure to change rapidly and in others causing the pressure to drift slowly up or down. These factors include age, weight, consciousness, blood volume, history of hypertension, and the like. The maintenance of the preselected blood pressure level is further complicated by the time-delayed response of the patient to Nipride. The effects of a given dose may not be observed for several minutes.
In most instances, the attending nurse also cares for other patients and must make adjustments as often as time permits. The drifting of the patient's blood pressure level between adjustments results in periods in which the patient's blood pressure is higher than the preselected range of blood pressure levels and periods in which it is lower than the desired range of blood pressure levels.
Heretofore, the experience of the attending nurse has been the primary factor in the accuracy with which the patient's blood pressure is controlled. Although the desirability of automatically controlling an infusion pump in response to the patient's blood pressure has been long recognized, the goal of controlling it within an acceptable range of blood pressure levels has been elusive.
The present invention contemplates an apparatus for automatically controlling the rate at which medication is introduced to the patient which overcomes the above-referenced problems and others. Yet, it provides a controller which controls infusion pumps and other medication introducing devices with a high degree of accuracy and reliability.